1. Field of the Invention
This invention relates to containers having a removable cover and from which the air can be at least partially evacuated.
2. Prior Art
For long-term storage of goods, it is known to form containers with a base, commonly rigid and which may be of pallet form, onto which base a cover may be sealed. Air is then evacuated from within the container. For many purposes, it is convenient to use a flexible impermeable cover such as is described for example in British Pat. No. 1,191,921. The periphery of the cover may be sealed into a groove or slot of a rigid impermeable base, the sealing being effected by means of an inflatable tube which may be integral with the cover or attached thereto or may be a separate tube located within the slot or groove as is described for example in U.S. Pat. No. 3,850,214. The tube, when inflated, presses the peripheral portion of the cover against one wall of the slot or groove.
It is the practice to use thick butyl rubber sheet to form such a flexible impermeable cover. When goods are stored for many years in such a container, it has proved necessary periodically to check the containers to ensure that there has been no leakage of air into the container. Such leakage might occur due to some very slight porosity in the flexible cover material or due to a slow leakage in the sealing arrangement.